Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$139.82	6.394%	$148.7601	$148.76	$148.75	$148.80
Purchase #2	$65.78	12.719%	$74.1466	$74.15	$74.15	$74.10
Purchase #3	$57.45	3.834%	$59.6526	$59.65	$59.65	$59.70
Purchase #4	$231.72	10.266%	$255.5084	$255.51	$255.50	$255.50
Purchase #5	$143.78	6.301%	$152.8396	$152.84	$152.85	$152.80
Purchase #6	$157.28	3.507%	$162.7958	$162.80	$162.80	$162.80
Purchase #7	$17.54	7.722%	$18.8944	$18.89	$18.90	$18.90
7 purchase totals =	$813.37		$872.5975	$872.60	$872.60	$872.60